BOSTON (AP) -- Al Horford's 7-year-old, Ean, sat in the front row of the postgame news conference, wearing a hat from last season's NBA Finals.
Up on the podium, his father needed no reminder of what Thursday night's game against the Golden State Warriors meant for the Celtics and their fans.
"Yeah, it's a big game," the Boston big man said after scoring 20 points with 10 rebounds and three blocked shots, making a key 3-pointer in overtime to help the Celtics beat the Warriors 121-118 in a finals rematch.
"You know, I wanted to come out here, and I wanted to win. I wanted to win really bad," Horford said. "It's a regular season. It's just one game. It's over. But it's an important game."
Jayson Tatum scored 34 points with a career-high 19 rebounds, following Horford's overtime 3 with one of his own to put Boston up by seven with 1:30 left. Jaylen Brown added 16 points, making a 3-pointer with 19 seconds left in regulation to send the game into overtime.
The victory snapped a four-game losing streak against Golden State -- the last three games of the finals and the first regular-season rematch, which the Warriors won in San Francisco in December.
"The fact of the matter is we lost. We lost the championship," Tatum said. "No one win -- we can't bring that back. We can't go back in time and change that.
"So we didn't look at this as a rematch of the finals," he said. "It's just one game."
Stephen Curry scored 29 points, Jordan Poole had 24 and Klay Thompson also had 24 before fouling out in overtime for the Warriors. The defending champions fell to 5-18 on the road this season.
"Disappointed that we didn't close the game, but I know we can do this," Warriors coach Steve Kerr said. "Better now than in the playoffs."
Boston led by as many as 10 in the first half but trailed for the entire second half before Brown's 3-pointer tied it. The Celtics scored the first four points of overtime but Draymond Green hit a pair of free throws and Curry sank a 3 to give the Warriors a 111-110 lead.
Brown made a floater to take back the lead, then Horford hit a 3-pointer and Tatum made his to give the Celtics a 118-111 lead with 1:26 to play. Boston got sloppy down the stretch to give Golden State a chance at the buzzer, but Poole's half-court shot wasn't close.
The Warriors won the finals in Game 6 in Boston, and then won the first rematch of the regular season in San Francisco. Although the Celtics have come out to the best record in the NBA this season, the losses to Golden State still rankle them.
Tatum struggled against the Warriors in June and scored 18 points on 6-for-21 shooting at Golden State on Dec. 10. But he credited Horford, who had 10 points, five rebounds and a chase-down blocked shot in the first period, with getting Boston off to a good start at home.
"Al came out and looked like he was 25 today," Tatum said. "He came out and set the tone, he really did. And we all kind of followed behind that the rest of the night."
Curry wowed the Boston crowd at the end of the first half with a buzzer-beater that was officially listed as 50 feet.
The Warriors had the ball with the clock running down, but Malcolm Brogdon stole it from Thompson and got it to Tatum. Curry took it away from him and lined up a 3-pointer from the far side of the halfcourt circle.
It swished through the net, giving the Warriors a 55-54 lead.
The Warriors led by as many as 11, 85-74, with two minutes left in the third, but Boston came back and tied it on Brown's 3. The Warriors opted not to call a timeout, and Curry dribbled out the clock before tossing a 3-point attempt that banged off the front of the rim. (The Celtics managed to get a timeout with 0.5 seconds left, but couldn't get off a shot.)
Brown was back for Boston after missing three games with a groin injury. Celtics center Robert Williams III missed the Dec. 10 game between the teams and was out for the first 29 games of the season recovering from left knee surgery.
With Curry returning on Jan. 10 from an 11-game absence (partially dislocated left shoulder), and Wiggins coming back earlier in the month after missing 15 games (strained muscle in right leg; non-COVID illness), both teams were relatively healthy.
Warriors: Thompson picked up his fifth foul and went to the bench with eight minutes left in the fourth. ... Wiggins scored 20. Green had 11 points, 13 rebounds and nine assists.
Celtics: Observed a moment of silence for Chris Ford, the former player and coach who died this week at the age of 74. ... Williams had 14 points and 11 boards. Smart scored 18. ... The Celtics shot 73% from the free throw line and under 40% from the field.